Abstract: To reveal the influence of temperature on the pore structure of fiber concrete, a series of NMR tests on basalt fiber concrete at different temperatures was carried out, focusing on the analysis of pore structure parameters, including porosity, T₂ spectrum distribution, pore size distribution, etc., and the fine morphological changes caused by high temperature were observed by scanning electron microscopy. The test results showed that the T₂ spectra of fiber concrete specimens at different temperatures showed a "ripple-like" fluctuation pattern, which indicated that the internal pore structure characteristics of the specimens changed significantly after experiencing high temperature; under high temperature, the number of large pore size pores of plain concrete, low-fiber-doped concrete and high-fiber-doped concrete increased in order, and the degree of pore structure deterioration increased in order. The pore structure degradation degree is aggravated; and with the increasing temperature, the pore number ratio of basalt fiber concrete and plain concrete is close to each other; the microscopic morphology of concrete analyzed by electron microscope scan intuitively shows that with the increasing temperature, the basalt fiber concrete experiences the evolution process of surface compacting, new pore constantly sprouting, pore width continuously enlarging, and series penetration, and finally developing into macroscopic fissures.

Key words: basalt fibre concrete, high temperature, fibre admixture, pore structure characteristics, deterioration, composites